1. Field of the Invention
The present invention relates to a novel rare earth-Fe—B-based permanent magnetic alloy with high magnetic properties having a TbCu7 hard magnetic phase as a main phase, particularly, an R—Fe—Co-M-B-based permanent magnetic alloy (wherein R is at least one rare earth element including Y with 70 at. % or more thereof being occupied by Sm, and M is at least one element selected from the group consisting of Nb, Ti, Zr, Hf, V, Mo, Cr, and Mn), and relates to a novel, high performance bonded magnet comprising the permanent magnetic alloy bonded with a binder.
2. Description of the Prior Art
Conventionally known rare earth magnet materials include Sm—Co-based magnet materials, Nd—Fe—B-based magnet materials, and Sm—Fe—N-based magnet materials. The Sm—Co-based magnet material is thermally little affected in its magnetic properties, but less practicable as isotropic magnet materials because the maximum energy product (BH)max is smaller than that of the Nd—Fe—B-based magnet materials. The Nd—Fe—B-based magnet material is now a main material for the rare earth bonded magnets because of their high magnetic properties, but has a drawback of a thermal change of magnetic properties larger than that of the Sm—Co-based magnet materials. The Sm—Fe—N-based magnet materials have magnetic properties comparable to those of the Nd—Fe—B-based magnet materials and have a merit of having magnetic properties thermally less affected than in the Nd—Fe—B-based magnet materials.
The demand for even more enhancing the performance of known rare earth magnet materials has become increasingly severe, and the magnetic properties thereof attained now appear to closely approach their limit. In view of these circumstances, a novel rare earth magnet material with high performance has been desired.
U.S. Pat. No. 5,716,462 discloses in Example 1 that an alloy hot melt corresponding to the following composition was quenched by ejecting it over a single cooling copper roll rotating at a peripheral speed of 40 m/s, thereby obtaining a thin alloy ribbon having a composition of Sm7.35Zr2.45Co26.5B1.88Febal. (B/Sm=0.26). The quenched thin alloy ribbon is then heat-treated in vacuum at 720° C. for 15 min. The result of X-ray diffraction on the thin alloy ribbon after the heat treatment shows diffraction peaks attributable to the TbCu7 phase (main phase) and minute α-Fe diffraction peaks. The thin alloy ribbon after the heat treatment is then pulverized in a mortar into powder having a particle size of 100 μm or less. After mixing the resultant powder of magnetic material with 2% by mass of an epoxy resin, the mixture is compression-molded under a pressure of 784 MPa. The molded body is cured at 150° C. for 2.5 h. The magnetic properties at room temperature of the bonded magnet thus prepared are 0.75 T for the remanent magnetic flux density Br, 210 kA/m for the coercive force Hcj, and 64 kJ/mm3 for the maximum energy product (BH)max.
U.S. Pat. No. 5,716,462 further discloses in Example 2 as follows. The thin alloy ribbon obtained above by heat-treating in vacuum at 720° C. for 15 min is pulverized into powder having a particle size of 32 μm or less, followed by a nitriding treatment (heat treatment) in a nitrogen gas atmosphere under 1 atm at 440° C. for 65 h to obtain a magnetic nitride powder having a composition of Sm6.76Zr2.25Co24.35B1.70N8.12Febal. (B/Sm=0.25). The content of fine powder having a particle size of 3.8 μm or less is reduced to 5% by volume or less of the magnetic nitride powder. After mixed with 2% by mass of an epoxy resin, the resultant powder of magnetic material is compression-molded under a pressure of 784 MPa. The molded body was cured at 150° C. for 2.5 h. The magnetic properties at room temperature of the bonded magnet thus prepared were 0.75 T for Br, 560 kA/m for Hcj, and 81 kJ/mm3 for (BH)max.
Upon comparing Examples 1 and 2 of U.S. Pat. No. 5,716,462, it can be found that the alloy composition of the powder of magnetic material has been so selected as to exhibit highest magnetic properties when subjected to the nitriding treatment. However, it has not been discovered that a novel permanent magnetic alloy having high magnetic properties, which substantially comprises a TbCu7 hard magnetic phase (main phase) and a fine crystal having an average crystal grain size of less than 5 nm and/or an amorphous phase, can be obtained by quenching a melt having a composition corresponding to that of the permanent magnetic alloy of the present invention to prepare a thin alloy ribbon, followed by a heat treatment in a non-oxidative atmosphere substantially free from nitrogen. In addition, it is not disclosed that the magnetic properties are significantly improved by regulating a B/R ratio (atomic % ratio) of the permanent magnetic alloy within the range of the present invention. In the present invention, it is important for enhancing the magnetic properties to limit a N content range of the permanent magnetic alloy. This important feature is also not disclosed therein.
International publication WO 99/50857 discloses in claim 18 a quenched alloy having TbCu7 crystal phase as a main phase and a composition represented by the following formula: R1XR2YBZT100-x-Y-Z, wherein R1 is at least one element selected from rare earth elements, R2 is at least one element selected from Zr, Hf and Sc, T is at least one element selected from Fe and Co, and X, Y and Z are numbers satisfying 2 at. %≦X, 0.01 at. %≦Y,4≦X+Y≦20 at. %, and 0≦Z≦10 at. %. However, the proposed quenched alloy requires a subsequent nitriding treatment to acquire intended magnetic properties. In this point, the proposed quenched alloy is distinguished from the permanent magnetic alloy of the present invention. Thus, WO 99/50857 fails to disclose the features of the permanent magnetic alloy of the present invention, namely, the micro structure comprising a TbCu7 hard magnetic phase (main phase) and a fine crystal having an average crystal grain size of less than 5 nm and/or an amorphous phase; the B/R ratio (atomic % ratio) regulated with the range of 0.30≦B/R≦2.5; and the nitrogen content regulated less than 0.1 at. %.
U.S. Pat. No. 5,968,289 discloses in claim 1 a permanent magnetic material having a TbCu7 crystal structure as the main phase and a composition represented by the following formula: R1xR2yAzOuBvM100-x-y-z-u-v, wherein R1 is at least one element selected from rare-earth elements including Y; R2 is at least one element selected from Zr, Hf and Sc; A is at least one element selected from H, N, C and P; M is at least one element selected from Fe and Co; and x, y, z, u and v are each atomic % defined by 2≦x, 0.01≦y, 4≦x+y≦20, 0.001≦z≦10, 0.01≦u≦2, and 0<v≦10. However, U.S. Pat. No. 5,968,289 fails to disclose the features of the permanent magnetic alloy of the present invention, namely, the specific micro structure and the B/R ratio (atomic % ratio) regulated within the range of 0.30≦B/R≦2.5.